1. Field of the Invention
This invention relates to a noise generation method and system, and more particularly to a shaped digital noise generation method and system.
2. Description of the Prior Art
Conventionally, digital noise generation is implemented by sampling an analog noise source, such as a noise diode, i.e., sampling white noise. However, digital noise generated by sampling white noise generally results in several undesirable effects. For example, analog noise sources display inconsistent unit-to-unit operation and relatively high failure rates, requiring frequent readjustments. In addition, thermal sensitivity inherent in analog noise sources may affect the consistency of the performance of the noise source rendering the quality of digital noise generated therefrom inconsistent over time.
Conventional digital noise generation also includes a method whereby multiple parallel taps off a single linear feedback shift register are used to develop a sequence of random digital word signals. The sequence of random digital word signals is provided to a frequency modulating synthesizer which translates the sequence to a digital noise signal. The frequency of the digital noise signal vary with each new word signal of the sequence. This approach, however, like the technique that consists of directly sampling white noise, has drawbacks. For example, varying the frequency of a digital noise signal in accordance with a generated sequence of digital word signals may produce an even frequency distribution with an uneven frequency rate distribution within the noise signal generated thereby. More specifically, the frequency rate distribution within the digital noise signal will reflect a gaussian rather than flat character for a particular frequency bandwidth mapped by the generated sequence. Thus, a desirable flat crossing rate distribution will not appear in the noise distribution and the power spectral density of the generated noise signal.